Apache logging problem

I'm working with an Apache server on Linux, and we recently started
having a strange problem with the logging. When you typically hit a
page with your browser, Apache will first log a request to the HTML
page (or PHP page, or whatever). It will then log all the requests your
browser makes for images on that page. The problem we are having is
that the request for the actual page is not getting logged. All the
requests for the images show up, but not for the actual page itself.
The pages that are having this problem are generated by PHP, although a
URL Rewrite hides this fact from the user. If the user were to hit a
page like www.oursite.com/folder/file.html, the URL Rewrite would cause
this to go to a php script in the form of
myscript.php?ruri=/folder/file.html. The php script then parses some
XML data from our content management system to actually produce the
page.

Now, I've noticed that this logging problem doesn't happen with all the
pages. There are some pages that generally get logged correctly (with
the hit to the HTML page - which is actually a hit to a PHP script)
getting logged along with the images. Other pages don't log this hit to
the HTML page. The only difference I can find between pages that work
and pages that don't is that they are using different XML templates. It
seems odd to me that the XML template a PHP script is parsing would
cause Apache to not log a hit to the page.

My only guess is that there is a problem in the PHP code, that causes
it to:
a) terminate with a strange error code, or
b) get into some sort of endless loop
when it encounters certain things in the XML, and because of that
Apache never logs the hit. The pages still seem to display correctly in
the browser, though, even if they don't get logged properly.

Has anyone encountered a problem like this before? Any suggestions on
what might cause a PHP script to not get logged by Apache?